Earpieces can be placed within human ears, e.g., as part of earphones, Bluetooth devices, etc., to deliver sound to the ears. To enhance sound quality and the user's acoustic experience, earpieces may be configured to enhance passive noise attenuation. For example, an earpiece may substantially seal the entrance of a user's ear canal so that sound delivered to the ear does not leak to the external environment, and so other sounds, e.g., the passive noise, from the environment, are substantially blocked. In another example, an earpiece may have an incomplete seal to allow for situational awareness. The earpiece may provide a desired level of acoustic leak.